The present invention relates to a shaft coupling having two attachment elements that are rotatable relative to one another and that are connected to one another by rotationally resilient assembly, and further having a dampening device which is active between the attachment elements for the purpose of suppressing torsional vibrations of the rotationally resilient assembly.
In the drivelines of motor vehicles there occur torsional vibrations which, especially in high-performance vehicles and four wheel drive vehicles, cannot be suppressed by conventional vibration dampening means at the clutch disc. Likewise, vibration dampening means additionally attached to the propeller shaft, for example, resiliently arranged absorber masses, often are not sufficient to prevent such vibrations from occurring.
It is therefore the object of the present invention to provide a shaft coupling that is incorporated into the driveline, has a high torque transmitting capacity and includes a highly effective dampening means.
According to a first embodiment, the rotationally resilient assembly comprises two ramp discs that are rotatable relative to one another and that support one another at least indirectly. One disc is supported in a rotationally fixed and rigid manner on one attachment element. The other disc is supported in a rotationally fixed and axially moveable manner on the other attachment element by a spring. The dampening device is a viscous coupling having a hub connected to one of the attachment elements and a housing connected to the other one of the attachment elements. The torsion spring and the torsion damper are systematically switched in parallel relative to one another.
In a preferred embodiment, the ramp discs include circumferential grooves having variable depths, in which balls are guided. Each circumferential groove has a deepest point and the depth of the groove decreases symmetrically from the deepest point towards both ends. Furthermore, the circumferential grooves of the discs are preferably arranged opposite one another as are the discs to thereby jointly accommodate a plurality of balls between them. The decrease in the groove depth as a function of the angle of rotation from the deepest point can be linear or progressive.
In a further preferred embodiment the spring comprises a plurality of plate springs. To achieve uniform load conditions, there are preferably provided three circumferentially distributed balls in the respective grooves to permit the ramp discs to rotate relative to one another in a low-friction way. The rotation of the ramp discs, which is converted into compression of the plate spring, can lead to a very high shaft stiffness of the coupling while at the same time achieving a short coupling length. To ensure effective dampening, there is provided a viscous coupling with suitable plates for generating a high dampening effect, i.e. there is provided an assembly which consists of a hub and a housing, which is filled with a highly viscous medium and which carries axially alternatingly arranged plates.
According to a further preferred embodiment, the ramp discs and the plate spring are arranged in the housing of the viscous coupling.
According to a second embodiment the rotationally resilient assembly comprises a torsion bar having one end connected in a rotationally fixed manner to one of the attachment elements and the other end connected in a rotationally fixed manner to the other one of the attachment elements. The dampening device is a viscous coupling whose hub is connected in a rotationally fixed manner to one of the attachment elements and whose housing is connected in a rotationally fixed manner to the other one of the attachment elements. The torsion bar needs to have a certain length because a hub-shaped attachment element can, at the same time, form the hub of the viscous coupling, i.e. as the torsion bar is arranged concentrically inside the viscous coupling, in this case, too, the overall assembly length is relatively small. The assembly has a very simple design. To ensure effective dampening, there is provided a viscous coupling with suitable plates for generating a high dampening effect, i.e. an assembly which consists of a hub and a housing, which is filled with a highly viscous medium and which carries axially alternatingly arranged plates.
According to a preferred embodiment the rotationally resilient assembly furthermore comprises a torsion tube spring arranged concentrically relative to the torsion bar. One end of the torsion tube spring is connected in a rotationally fixed manner to one of the attachment elements and that the other end of the torsion tube spring is freely rotatable relative to the other attachment element up to a limited rotational angle. In this way it is possible, from a certain angle of rotation onwards, to achieve a high degree of torsional stiffness, without the design of the shaft coupling becoming particularly complicated. In this embodiment also, the torsion bar, the torsion tube spring and the viscous coupling are arranged coaxially relative to one another to reduce the length of the assembly.
Preferred embodiments of the invention will be described below in greater detail with reference to the drawings.